MINIMUM HARDWARE CONSIDERATIONS

If the A/D converter will be used, connect VREF to a separate reference supply to minimize noise during A/D conversions. Even if the A/D converter will not be used, VREF and ANGND must be connected to provide power to port 0. On the 8XC196MC and MD, they also provide power to port 1. Refer to “Analog Ground and Re ference Voltages” on page 12-12 for a detailed discussion of A/D power and ground recommendations.

Multilayer printed circuit boards with separate VCC and ground planes also help to minimize noise. For more information on noise protection, refer to AP-125, Designing Microcontroller Sys- tems for Noisy Environments and AP-711, EMI Design Techniques for Microcontrollers in Auto- motive Applications.

13.4 THE ON-CHIP OSCILLATOR CIRCUITRY

The on-chip oscillator circuit (Figure 13-3) consists of a crystal-controlled, positive reactance os- cillator. In this application, the crystal operates in a parallel resonance mode. The feedback resis- tor, Rf, consists of paralleled n-channel and p-channel FETs controlled by the internal powerdown signal. In powerdown mode, Rf acts as an open and the output drivers are disabled, which disables the oscillator. Both the XTAL1 and XTAL2 pins have built-in electrostatic discharge (ESD) pro- tection.

To internal

circuitryVCC

XTAL1

(Input)

Rf

XTAL2

(Output)

Oscillator Enable# (from powerdown circuitry)

VSS

A0076-03

Figure 13-3. On-chip Oscillator Circuit

13-5

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Image 290
Intel 8XC196MC, 8XC196MD, 8XC196MH manual ON-CHIP Oscillator Circuitry, On-chip Oscillator Circuit